lockf - apply, test or remove a POSIX lock on an open file
int lockf(int fd, int cmd, off_t len);
Apply, test or remove a POSIX lock on an open file. The file is specified
by fd. This call is just an interface for fcntl(2). Valid operations
are given below:
F_LOCK Set an exclusive lock to the file. Only one process
may hold an exclusive lock for a given file at a given
time. If the file is already locked it blocks until
the previous lock is released.
F_TLOCK Same as F_LOCK but never blocks and return error
instead if the file is already locked.
F_ULOCK Unlock the file.
F_TEST Test the lock: return 0 if fd is unlocked or locked by
this process; return -1, set errno to EACCES, if
another process holds the lock.
On success, zero is returned. On error, -1 is returned, and errno is
EAGAIN The file is locked and the LOCK_NB flag was selected, or operation
is prohibited because the file has been memory-mapped by
EBADF fd is not an open file descriptor.
EDEADLK [Toc] [Back]
Specified lock operation would cause a deadlock.
EINVAL An invalid operation was specified in fd.
ENOLCK Too many segment locks open, lock table is full.
There are also locks.txt and mandatory.txt in /usr/src/linux/Documenta-
Linux 2.0 1997-08-06 LOCKF(3)
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